Radon and Thoron Exhalation Rates from Surface Soil of Bangka - Belitung Islands, Indonesia

  

Indonesian Journal on Geoscience Vol. 2 No. 1 April 2015: 35-42

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Radon and Thoron Exhalation Rates from Surface Soil of Bangka - Belitung Islands,

Indonesia

  

Syarbaini and E. Pudjadi

Center for Technology of Radiation Safety and Metrology, National Nuclear Energy Agency

Jln. Lebakbulus Raya no. 49, Jakarta 12440, Indonesia

  

Corresponding author: sarbaini@batan.go.id

Manuscript received: September 21, 2014, revised: January 27, 2015, approved: April 02, 2015,

available online: April, 08, 2015

  Abstract - Radon and thoron exhalation rate from soil is one of the most important factors that can influence the radio-

activity level in the environment. Radon and thoron gases are produced by the decay of the radioactive elements those

are radium and thorium in the soil, where its concentration depends on the soil conditions and the local geological

background. In this paper, the results of radon and thoron exhalation rate measurements from surface soil of Bangka

Belitung Islands at thirty six measurement sites are presented. Exhalation rates of radon and thoron were measured

by using an accumulation chamber equipped with a solid-state alpha particle detector. Furthermore, the correlations

_{226 232}

between radon and thoron exhalation rates with their parent nuclide ( Ra and Th) concentrations in collected soil

samples from the same locations were also evaluated. The result of the measurement shows that mostly the distribution

_{226 232}

of radon and thoron is similar to Ra and Th, eventhough it was not a good correlation between radon and thoron

_{226 232} exhalation rate with their parent activity concentrations ( Ra and

  Th) due to the environmental factors that can influ- _{222 220}

ence the radon and thoron mobilities in the soil. In comparison to a world average, Bangka Belitung Islands have the

Rn and Rn exhalation rates higher than the world average value for the regions with normal background radiation.

  Keywords: radon, thoron, exhalation rate, soil, Bangka-Belitung How to cite this article:

Syarbaini and Pudjadi, E., 2015. Radon and Thoron Exhalation Rates from Surface Soil of Bangka - Belitung Islands,

Indonesia . Indonesian Journal on Geoscience, 2 (1) p.35-42. DOI:10.17014/ijog.2.1.35-42 ₂₂₂

  andan and Sathish, 2011). Rn having an atomic

  Introduction _{222 220} number of 86, is the heaviest member of the rare

  Radon ( Rn) and thoron ( Rn) are radioac- gas group ( 100 times heavier than hydrogen ₂₂₆ ∼ ₂₂₀ tive gases produced by the decay of Ra and and 7.5 times heavier than air). Rn is an ₂₂₄

  ∼

  Ra, which are themselves the decay products of _{238 232} isotope of radon, that has an atomic number of 86, U and Th series in the ground, respectively. _{222 220} and mass number of 220. The main characteristic _{222 220} Rn and Rn decay with the emission of alpha of Rn and Rn among the other natural radio- particles and produce daughter nuclei - polonium

  IJOG _{218 216 214 212 214 212 210} active elements is the fact that their behaviour is

  ( Po, Po, Po, Po), lead ( Pb, Pb, Pb), _{214 212 210} chemically inert (noble gases), not affected by _{222 220} and bismuth ( Bi, Bi, Bi). These daughter ₂₂₂ chemical processes. The Rn and Rn are free nuclei emit alpha or beta particles. Rn has a to move through soil pores and rock fractures; ₂₂₂ half-life of 3.825 days and is an alpha emitter; _{220 220} then to escape into the atmosphere. Rn and/or

  Rn has a half-life of 55.6 s and is also an alpha Rn exhaled from the earth surface into the free emi tter (Figure 1) (Por stendorfer, 1994; Ramach- atmosphere is rapidly dispersed and diluted by

  

IJOG/JGI (Jurnal Geologi Indonesia) - Acredited by LIPI No. 547/AU2/P2MI-LIPI/06/2013, valid 21 June 2013 - 21 June 2016

  

Indonesian Journal on Geoscience, Vol. 2 No. 1 April 2015: 35-42

  6.13 h 3.66 d 55.6 s 0.15 s

  Figure 1. Decay Series of ²³⁸ U (a), and ²³² Th (b) (HASL-300, 1997) .

  232 (b) Th Decay Series

  (a) U Decay Series 238

  β decay α decay α decay

  1.64 x 10 s ^{4 4} 754 x 10 y 19.9 min ¹⁰ β decay

  5.013 d Stable 138.376 d 3.05 min

  1.41 x 10 y 1600 y 3.825 d 26.8 min 22.3 y

  3.053 min 310 ns Stable 10.64 h 60.6 min

  24.1 d 5.75 y 1.91 y

  natural convection and turbulence (Mudd, 2008; Hassan et al., 2011). ₂₂₂ Rn and ²²⁰ Rn in the ambient air depend on the soil conditions and the local geological background. ²²² Rn and ²²⁰ Rn emanate mainly from the earth surface through the gap in soil to the atmosphere. ²²² Rn and ²²⁰ Rn gases enter the house from various gaps in walls and open win- dows or doors. They decay producing isotopes of polonium ( ₂₁₂ ²¹⁸ Po, ²¹⁶ Po, ²¹⁴ Po, ²¹² Po), lead ( ²¹⁴ Pb,

  214 Pb ²¹⁰ Pb ²¹⁰ Bi ₂₀₆ Pb ²¹⁰ Pb ²¹⁸ Po ²¹⁴ Po ₂₁₄ Bi ²³⁰ Th

  226 Ra ₂₂₂ Rn

  208 Tl ²¹² Po ₂₀₈ Pb ²¹² Pb ²¹² Bi ²³² Th

  U ²³⁴ U _234m Pa ⁹ 4.47x10 y ^{5 10} 4.45x10 y ₂₃₄ 117 min Th ²²⁸ Ra ²²⁸ Th ₂₂₈ Ac ₂₂₄ Ra ₂₂₀ Rn ₂₁₆ Po

  Generally, when the ²²⁶ Ra and ²³² Th are high, the exhalation rates of ²²² Rn and ²²⁰ Rn at that site are a relatively high too. Therefore, this study was conducted with the ²²² Rn and ²²⁰ Rn exhalation rates from the ground surface in Bangka-Belitung. The objective of this work is to determine ²²² Rn and ²²⁰ Rn exhalation rates from the soil surfaces of Bangka – Belitung Islands and to evaluate the correlation with their parent radionuclides ( ^{238 226} Ra and ²³² Th). The study will

  Belitung Islands are known as tin producer plac- es which form a part of Southeast Asia Tin Belt, the richest tin belt in the world which stretches along South China - Thailand - Myanmar - Malaysia to Indonesia (Schwartz et al., 1995). Meanwhile, there are some other mineral re- sources like: quartz sand, building construction sand, kaolin, granite, clay, and mountain stone. The geology of Bangka Belitung is structured by granites (hard stone). Itis generally covered by klabat granite which are devided into three catagories, i.e. biotite granite, granodiorite, and gneissic granite. The soil derived from granite will have a higher radioactivity than the soil from the other rock types (Saleh and Ramli, 2013: Rani and Singh, 2005).

  Bangka and Belitung Islands have the geo- logical potential of mineral resources, especially tin, with accessory minerals consisting of mona- zite, zircon, xenotim, ilmenite, magnetite, and pyrite spreading in almost all regions. Bangka

  Pb, ²¹⁰ Pb), and bismuth ( ²¹⁴ Bi, ²¹² Bi, ²¹⁰ Bi) which are heavy metals chemically very active, that may exist briefly as ions and/or free atoms before forming molecules in a condensed phase or attached to airborne dust particles, forming radioactive aerosols. This fraction may be inhaled and deposited in the respiratory tract, in which they release all their α-emissions. It is, therefore, important to know the ²²² Rn and ²²⁰ Rn exhalation, and these information are useful for presumption of a high ²²² Rn- ²²⁰ Rn concentration area.

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Radon and Thoron Exhalation Rates from Surface Soil of Bangka - Belitung Islands, Indonesia

(Syarbaini and E. Pudjadi)

  Rn and ²²⁰ Rn accumulation chambers is con- nected to the RAD7 detector by vinyl tubing with a gas-drying unit filled with a desiccant (CaSO ₄ with 3% CaCl ₂ ) to maintain the relative humidity at <10% within the measurement system. The system is a closed loop in which the gas circulates continuously.

  80 _{Ranggam Formation Kelapakampit Formation Quartz Diorite Baginda Adamelite Tanjungpandan Granite Burungmandi Granodiorite} Pemali Complex ^{Tanjunggenting Formation Klabat Granite Tajam Formation Quartz Sandstone Pangkal Pinang City} _{Central Bangka} South Bangka ^{Belitung North Bangka}

  40 S E N W

  

105 30' 106 106 30' 107 107 30' 108 E

^o _o o o _o o

^{o o o o o o}

^{EXPLANATION: GEOLOGY} kilometers ^{Center Part of Interest Area Interest Area Small River Main River Lake}

  2 2 30' 3 3 30' S

  105 E 1 30' S

  The accumulation chamber was placed on the ground surface from its open side, and its surroundings were covered to prevent any air exchange with environment. Tamping down the soil around the chamber is to prevent the leak- age of fresh air into the sample acquisition path or down the outside of the chamber to sampling point. Following the localization of the measured points using GPS devices and clearing the rel- Figure 2. The geology map of Bangka Belitung (IAEA, 2011).

  equipped with a solid state alpha detector (RAD7, Durridge Co. Inc., Bedford, MA, USA). The ac- cumulation chamber made of stainless steel as ₂₂₂

  help in understanding the status of indoor and outdoor ²²² Rn, ²²⁰ Rn and the status of the exhala- tion of these gases from soil in Bangka-Belitung.

  3), produced by Durridge Company Inc. (2010),

  In this study, the method for ²²² Rn and ²²⁰ Rn exhalation rate measurement is based on small accumulation chambers connected to a continu- ous Ra don Gas Monitor, model RAD7 (Figure

  Measurement of ²²² Rn and ²²⁰ Rn Exhalation Rates from Surface Soil

  The field study was performed on thirty six sampling sites where twenty eight sites were at Bangka Island and ten sites were at Belitung Island. Geographical coordinates of the sampling points were determined using GPS Map 60CHx manu- factured by Garmin. After finding the measuring site, any grass, gravel, and roots were removed to perform the measurements of ²²² Rn and ²²⁰ Rn exhalation rates. Then, at least 2 - 3 kg of soil was collected at each point using shovel and scoop. At a collection point the soil sample was wrapped in black plastic bag and then taken to the laboratory.

  Material and Methods Material

  Bangka-Belitung Islands are located at 104° 50’ - 109° 30’ E and 0° 50’ - 4° 10’ S which lie in east of Sumatra, northeast of South Sumatra Provinc e (Figure 2).

  This type of study has never been done before in Bangka Belitung Islands.

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Indonesian Journal on Geoscience, Vol. 2 No. 1 April 2015: 35-42

    ....................................... (1)

    

  A C f e

  ............................................ (2) M t P N

  s ^-1 and 144 -9470 mBq.m ^-2 .s ^-1 , respectively. The arithmetic average value of the ²²² Rn and ²²⁰ Rn

  The measurement result of ²²² Rn and thoron exhalation rates is show n in Table 1. It can be seen in Table 1 that ²²² Rn and ²²⁰ Rn exhalation rates were in the range of 3.73 - 326 mBq.m

• ^-2 .

  Result and Discussion

  = the gamma ray emission probability (gamma yield) at energy E, t _c = sample counting time, M = mass of sample (kg).

  γ

  where: N _e = net counts of a peak at energy E, ε _f = the counting efficiency of the detector system at energy E, P

  et al., 2014):

  Bq kg ^-1 for the samples were determined using the following expression (Knoll, 2000; Syarbaini

  The gamma energy peaks 352 keV of ²¹⁴ Pb and 609.31 keV of ₂₂₆ ²¹⁴ Bi were used to determine Ra. The gamma energy peaks of 238.6 keV from ²¹² Pb, 911.2 and 969 keV gamma energy peak from ²²⁸ Ac and 583 keV gamma energy peak from ²⁰⁸ Tl were used to determine the ²³² Th. The activity concentrations (A) of ²²⁶ Ra and ²³² Th in

  Ra and ²³² Th, and their short-lived daughters before measurement.

  keV (full width at half maximum) for the peak of 1,33 keV. In the laboratory, the soil samples were dried in an oven at a temperature of 105 C to a constant weight to remove any available moisture. After being dried, the samples were crushed and sieved with a mesh having holes each of diameter of 2 mm in order to remove organic materials, stones, and lumps. Afterwards, the homogenized samples were packed to fill 1 liter marinelli beakers. The marinelli beakers were carefully sealed in order to prevent trapped radon gas from escape and allowed to stand for at least four weeks for secular equilibrium to be estab- lished between the long-lived parent nuclides of ₂₂₆

   

  evant surface of any grass, gravel, and plant roots, the ²²² Rn and ²²⁰ Rn exhalation rate was measured. It is noteworthy that the environmental param- eters such as temperature, pressure, and relative humidity were recorded by the device during the period of measuring each site.

  V Cx E 

  S e

  ) 1 ( t

  Figure 3. The RAD7 system and accumulation chamber.

  The measurement of ²²⁶ Ra and ²³² Th in the soil samples collected from the same site with ²²² Rn and ²²⁰ Rn exhalation rates were carried out at a laboratory by using ORTEC P-type coaxial high purity Germanium (HPGe) detector with a rela- tive efficiency of 60% and a resolution of 1.95

  Measurement of ²²⁶ Ra and ²³² Th in Surface Soil

  S is the sample surface area (m ² ).

  ), and

  V is the effective air volume (m ³

  λ is the decay constant (s ^-1 ),

  thoron less the background concentration) at accumulation time t (Bqm

• ^-3 ),

  C is the net concentration (exhaled radon/

  Rn exhaled from the sample increases expo- nentially until radioactive secular equilibrium is reached. The exhalation rate (E ) from the sample can be calculated with equation (Tuccimei et al., 2006; Hassan et al., 2011): where:

  The changes in the ²²² Rn and ²²⁰ Rn concen- tration in the chamber were used as a function of time to estimate the exhalation rate from the ground surface. The concentration of ₂₂₀ ²²² Rn and

  IJOG

  

Radon and Thoron Exhalation Rates from Surface Soil of Bangka - Belitung Islands, Indonesia

(Syarbaini and E. Pudjadi)

Table 1. Radon and Thoron Exhalation Rates from Surface Soil in Bangka-Belitung Islands

  exhalation rates by all thirty six data were ob- tained to be 48.11 mBq.m

• ^-2 . s ^-1

  , 2008 mBq.m ^-2 . s ^-1 , respectively. The distribution of ²²² Rn and ²²⁰ Rn exhalation rates was indicated in Figure 4.

  This figure shows that ²²² Rn and ²²⁰ Rn exhalation rates vary widely from site to site.

  Site GPS Radon-Thoron Exhalation Rate (Bq m

• ^-2 s ^-1

  ) Parent Nuclide Concentrations (Bq/kg) S E ²²² Rn ²²⁰ Rn ²²⁶ Ra ²³² Th

1. 2.05341 105.96299 97.94 ± 19.04 177 ± 26 39.0 ± 2.6 75.7 ± 2.1

2. 1.92487 105.73072 3.73 ± 0.58 194 ± 29 26.2 ± 2.0 21.3 ± 1.6

3. 1.86887 105.55734 20.00 ± 3.54 196 ± 29 16.8 ± 1.3 28.0 ± 0.9

4. 1.90731 105.38345 42.93 ± 7.23 927 ± 137 116.3 ± 7.2 219.7 ± 5.9

5. 2.05292 105.17896 24.08 ± 3.46 947 ± 140 136.4 ± 8.5 601.2 ± 33.3

6. 2.02674 106.11205 17.98 ± 3.78 303 ± 45 29.5 ± 2.1 62.5 ± 1.8

7. 1.83548 106.09581 33.84 ± 4.78 4659 ± 691 143.7 ± 9.0 377.4 ± 10.2

8. 1.74349 105.93686 13.37 ± 2.85 2696 ± 400 80.6 ± 5.1 252.6 ± 6.8

9. 1.65345 105.80455 18.52 ± 3.34 3902 ± 579 76.7 ± 5.1 231.0 ± 6.6

10. 2.42239 106.30708 5.63 ± 1.31 1106 ± 210 63.0 ± 4.1 151.7 ± 4.2

  

11. 2.48396 106.41884 34.95 ± 6.06 162 ± 24 23.0 ± 1.6 44.3 ± 1.3

12. 2.61175 106.36892 291 ± 53 9470 ± 1404 543.8 ± 36.3 2170 ± 65.2

13. 2.79730 106.41721 61.03 ± 9.05 1644 ± 244 118.4 ± 7.4 510.8 ± 13.6

14. 3.00411 106.47252 20.27 ± 1.86 1969 ± 419 91.2 ± 5.9 109.0 ± 6.4

15. 2.99088 106.60519 48.21 ± 6.33 1875 ± 529 54.5 ± 3.6 115.0 ± 0.5

16. 2.70761 106.30343 7.96 ± 1.29 895 ± 168 64.4 ± 4.3 155.0 ± 4.3

17. 2.72320 106.17023 14.12 ± 1.60 564 ± 84 43.2 ± 3.8 77.8 ± 5.2

18. 2.61162 106.15139 46.43 ± 5.91 855 ± 127 46.0 ± 3.1 97.4 ± 2.7

19. 2.55059 106.48337 20.42± 1.97 3539 ± 864 42.1 ± 2.9 123.6 ± 3.4

20. 2.55455 106.64125 58.76 ± 10.23 1648 ± 487 99.6 ± 6.9 158.9 ± 4.6

21. 2.04609 105.76947 7.58 ± 1.52 3077 ± 813 115.2 ± 7.3 206 .8 ± 11.6

22. 1.99569 105.65130 19.32 ± 1.85 144 ± 21 25.4 ± 1.9 81.4 ± 2.3

23. 1.72616 105.45825 8.00 ± 1.47 164 ± 24 29.2 ± 2.0 59.0 ± 1.7

24. 1.64023 105.51582 30.46 ± 5.18 194 ± 29 22.9 ± 1.7 33.2 ± 1.0

25. 1.59386 105.57115 18.48 ± 3.14 3181 ± 825 61.6 ± 4.1 230.6 ± 13.8

26. 2.41710 106.05264 84.14 ± 17.72 5848 ± 1102 139.6 ± 8.5 412.7 ± 10.7

27. 2.76905 107.71902 22.15 ± 2.91 214 ± 32 71.8 ± 4.7 90.9 ± 2.6

28. 2.80287 107.76521 22.22 ± 3.03 2527 ± 617 68.3 ± 4.5 212.0 ± 6.0

29. 2.92091 107.82620 111 ± 11 4306 ± 947 194.8 ± 12.2 492.8 ± 28.7

30. 3.02891 107.89948 4.40 ± 0.63 254 ± 32 10.7 ± 0.9 18.4 ± 0.6

31. 3.09563 107.99509 87.18 ± 8.86 1820 ± 270 178.2 ± 11.0 376.7 ± 10.2

32. 2.70687 107.65446 18.07 ± 3.60 183 ± 27 57.6 ± 3.7 94.0 ± 2.6

33. 2.92137 108.18832 35.78 ± 3.43 1353 ± 256 89.5 ± 5.7 188.2 ± 5.1

34. 2.70462 108.02458 43.93 ± 7.44 3708 ± 550 101.5 ± 6.3 328.4 ± 19.1

35. 3.19425 107.59635 12.12 ± 1.43 199 ± 53 46.8 ± 3.1 99.6 ± 2.8

36. 2.75909 107.82616 326 ± 19 7398 ± 1097 258.1 ± 15.7 653.8 ± 38.0

  Range 3.73 – 326 144 – 9470 10.7 – 543.8 18.4 - 2170 Average 48.11 2008 92.38 254.5

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Indonesian Journal on Geoscience, Vol. 2 No. 1 April 2015: 35-42

10000 1000

  Radon Exhalation Rate

  2 (mBq/m .s) 100

  Thoron Exhalation Rate

  2 (mBq/m .s)

  10

1 Site No.

  1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 Figure 4. The distribution graph of radon and thoron exhalation rate levels. ₂₂₂

  Rn exhalation rate Seventy five percent of

• _-2 350 measurement results are more than 10 mBq.m . _{-1 -2}

  300 y = 0,563x

  s and 8.3 % of its are more than 100 mBq.m .

• _-1
• _{-1 250} R = 0,6716

  s , however 7.5 % of its are lower than 10 _{-2 -1 220 -2} mBq.m . s . Most of Rn exhalation rates are ₂₂₂ 200 higher than Rn exhalation rate, where 47.2 %

• _{-2 -1} (mBq.m .s ) 150

  of its are more than 100 mBq.m .s and 52.8

  Radon Exhalation Rate 100

  % of results had a exhalation rate of more than _{-2 -1 220} 1000 mBq.m . s . It was admitted that the Rn

  50 ₂₂₂ exhalation rate was about forty two times of the 200 400 600 Rn exhalation rate. _{226 -1 222 220} Ra Concentration (Bq.kg )

  In order to evaluate how Rn and Rn exha- ₂₂₂

  Figure 5. Correlation between Rn exhalation rate and

  lation rates are influenced by the activity concen- _{226 232 226} parent Ra concentration. tration of their precursors ( Ra and Th, respec- _{222 220} tively), the variation of Rn and Rn exhalation rates were observed to variations of radium and

  14000 y = 5,7358x

  thorium concentrations in soil collected from the _{226 232 R = 0,5121} 12000

  2

  same site. The concentration of Ra and Th

  10000

  in soil samples collected from the same measure- _-1

  8000

  ment sites were shown in Table 1, columns 6 and _{226 232 -2}

  7. Generally, the distribution of Ra and Th in _{222 220 on Exhalation Rate (Bq.m .s )} 6000 soil showed the same tendency as Rn and Rn

  IJOG 4000

  Thor

  distribution. By using its concentration levels, ₂₂₂

  2000

  the correlation between the Rn exhalation rate _{226 220} and the Ra concentration and between the Rn ₂₃₂

  1000 2000 3000

  exhalation rate and the Th concentrations were

  232 -1 Th Concentration (Bq.kg ) presented as in Figures 5 and 6. ₂₂₀

  As can be seen in Figures 5 and 6, it was

_{222 232}

Figure 6. Correlation between Rn exhalation rate and parent Th concentration. found a weak correlation between the Rn

  

Radon and Thoron Exhalation Rates from Surface Soil of Bangka - Belitung Islands, Indonesia

(Syarbaini and E. Pudjadi)

Figure 7. Comparison of ²²² Rn and ²²⁰ Rn exhalation rates in Bangka-Belitung with worldwide average values.

  Rn and/or ²²⁰ Rn exhaled from the surface soil may migrate into the structure of dwelling and accumulate indoors in sufficient quantities to pose a health hazard. WHO (2009) has classified them as carcinogenic to humans and the second most important cause of lung cancer after cigarette smoking. WHO (2009) recommended the levels of radon in the residental buildings as 100 Bqm

• ^-3 .

  Average Radon Exhalation Rate Thoron Exhalation Rate

  2500 Radon and Thor on Exhalation Rate (mBq m s- ) ^{2 1} Bangka-Belitung Woeldwide

  500 1000 1500 2000

  geology of Bangka Belitung Islands is covered by granite which has a higher radioactivity con- centration level than the soil from the common areas world average. Due to high level of ²²² Rn and ²²⁰ Rn exhalation rates in some areas of the

  The ²²² Rn and ²²⁰ Rn exhalation rates from surface soil of Bangka and Belitung Islands have been determined in situ measurement by using an accumulation chamber equipped with a solid-state alpha particle detector of RAD7. Then, the activ- ity concentrations of parent radionuclides ( ²²⁶ Ra and ²³² Th) in soil samples collected from the same site have been determined in the laboratory by us- ing gamma-ray spectroscopy. The result of mea- surement showed that ²²² Rn and ²²⁰ Rn exhalation rates as well as activity concentrations of ²²⁶ Ra and ²³² Th varied widely from site to site. Mostly, the distribution of ²²⁶ Ra and ²³² Th showed the same tendency as ²²² Rn and ²²⁰ Rn distribution, but it was not any strong correlation due to the influ- ence of environmental factors, such as weather, water content of soil, pressure, temperature, and humidity conditions. All the measurement result showed that the ²²⁰ Rn exhalation rate was higher than the ²²² Rn exhalation rate. From this study, it was also found that Bangka Belitung Islands have the ²²² Rn and ²²⁰ Rn exhalation rate higher than the wor ld average value reported by UNSCEAR. The

  Conclussion

  Belitung Island s (Figure 7) must be considered to assess the radiological hazard of living in these areas. ₂₂₂

  exhalation rate and the radium concentration (R = 0.67), and between the ²²⁰ Rn exhalation rate and the thorium concentration (R = 0.51).

  , respectively. Thus, the obtained value in this study were twice of values shown in UNSCEAR (2000) report. This fact suggests that the ²²² Rn and ²²⁰ Rn exhalation rates in Bangka-

  Rn exhalation rates are 26.2 mBq.m ^-2 . s ^-1 and 1000 mBq.m

• ^-2 .s ^-1

  In comparison to a world average, the results indicate that the ²²² Rn and ²²⁰ Rn exhalation rates for the studied area are much higher than the worldwide average. UNSCEAR (2000) report shows that the world averages of the ₂₂₀ ²²² Rn and

  At the measurement day, the soil condition was different from each other such as dry, semi- moist, and wet. The weather conditions on the day of measurement were partly cloudy, partly sunny, and cloudy. Based on the conducted studies, it was observed that with reduced soil moisture and ₂₂₀ weather conditions changing into sunny, ²²² Rn and Rn exhalation rates increase.

  (2007) reported that the exhalation rate showed a decreasing tendency for the increase in the moisture content over 8 %.

  (2004), the main factors influencing ²²² Rn diffusion in soil are the soil characteristics such as soil porosity and moisture. Advection takes place when there is pressure difference between the airs of pore space and ground surface. The most important factor affecting advection is the soil permeability. Other meteorological parameters like temperature difference between soil and surface air, wind velocity, and rainfall also affect the advection process. Hosoda et al.

  The weak correlation may be influenced by environmental factors, such as weather, water content of soil, and geology. According to Sun et al.

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Indonesian Journal on Geoscience, Vol. 2 No. 1 April 2015: 35-42

BangkaBelitung Islands, necessary provisions should be considered for construction in these areas to avoid ²²² Rn and ²²⁰ Rn entrance into resi- dential buildings.

  Hosoda, M., Shimo, M., Sugino, M., Furukawa, M., and Fukushi, M., 2007.Effect of Soil Mois- ture Content on Radon and Thoron Exhalation.

  Atom Indonesia, 40 (1), 27pp.

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